One of the questions Emma Brockes deals with in her recently released memoir, She Left Me the Gun, is how to tell a horrific story in a way that is not exploitative, sentimental, or “schmaltzy”, a story she knows would otherwise make “too great a demand on the reader”.

Her answer to this is humour, a kind of caustic wit she shares with her late mother, whose turbulent childhood is the book’s main subject.

When we meet, she appears calm, her manner candid and matter of fact. As recently as six months ago she was still uncomfortable with much of the book’s material: “I couldn’t imagine how I was going to do publicity. There were certain words I couldn’t say because I knew they would set me off. But all of this has been resolved now.”

When Brockes was 10, her mother, Paula, said to her: “One day I will tell you the story of my life and you will be amazed.”

Brockes knew her mother had grown up poor in South Africa, had lost her own mother to tuberculosis at the age of two, and had emigrated alone to England in her 20s. But beyond that, her mother’s life before her birth was a mystery, hints of a dark past occasionally finding their way to the surface.

“When the topic of South Africa came up when I was growing up, the temperature of the room would drop,” Brockes tells me. “At the time my mum would have explained that as being a function of apartheid, because no right thinking person had a good attitude towards South Africa. But it obviously wasn’t that. All of her background was covertly present in the way we talked, or rather the way we didn’t talk, about South Africa.”

Brockes says for a long time she was content with ignoring her mother’s “other past”. It is only when Paula is dying of cancer, and tells Brockes she once had her father arrested on charges of sexual abuse, that she can no longer remain ignorant: “I wasn’t in the position where I could un-know what I already knew. I was in a halfway house position which is completely untenable. You can’t half-know something.”

After Paula dies, Brockes travels to South Africa. Trawling through South Africa’s notoriously disorganised archives, she learns that her grandfather, James (Jimmy) deKiewit, was a convicted murderer. After speaking to Paula’s seven step-siblings and other relatives, she pieces together a picture of Jimmy as a violent alcoholic and a child molester.

Brockes recalls lying on the couch in the house in which she was staying in Johannesburg, “just staring at the wall in a catatonic state: I must have been in a total shutdown with all of this stuff. But I wasn’t depressed. I was energised by it all. It was thrilling as well as horrifying.”

When she could “see enough to see the whole”, she went home “happy as a clown until I sat down and had to try and figure out how to write it.”

It was only years later that she felt ready to write the story: “It took me years to be able to find a language to talk about it in.”

The title of the book refers to the handgun Paula took with her to England and kept “wrapped in a pair of knickers” in a “secret drawer”. It was the gun she had used to try to kill her father with and she wanted Brockes to have it one day. While Brockes doesn’t ever get the gun, it is more important as a symbol than as an object. What Paula bequeaths to Brockes is the strength and resilience it represents; her refusal to let her daughter see her as fragile.

Brockes tells this difficult story in a way that makes her likeable both on the page and in person.

She describes the book as an “anti-misery memoir”, as the story of strong women rather than the story of their vulnerability at the hands of an abusive father.

“I wanted it to be about other things too,” she says, “like mothers and daughters and families. It’s a love story as well as a very gruesome story.”

When I ask if she has accepted her mother’s past as part of her own identity, she assures me she has grown comfortable with being “one-quarter psychopath. The reason I’m saved from internalising all the awfulness too much is that my mum was a hero. What I really get from the story is that she was an amazing person. I’ll take that. And the rest can go f–k itself.”